Technical Abstract:
In studies of the mode of action of microbial acetylxylan esterases on fully and partially acetylated derivatives of methyl beta-D- xylopyranoside and -glucopyranoside, the products of partial deactylation were first converted to their O-trimethylsilyl (TMS) ethers, separated by GLC and then identified by EI MS. At an ionization potential of 70 eV, a great similarity in the pattern of fragmentation was observed for TMS derivatives of methyl beta-D- xylopyranoside diacetates and methyl beta-D-glucopyranoside triacetates containing an acetylated C-6 hydroxyl group. Even greater similarity was observed in the fragmentation pattern of methyl beta-D- xylopyranoside monoacetates and methyl beta-D-glucopyronaside diacetates containing the C-6 acetyl group. The examination of the generated fragments pointed out that the energy of 70 eV is sufficient not only for removal of acetyl fragment ions, but also for removal of acetylated C-6 hydroxymethyl group of the glucopyranosides to form first an analogue of the aldopentaose derivative. The assignments of the major fragments observed in the spectra pointed out that the fragments originate mainly in molecular regions containing more stable TMS groups. The fragmentation patterns for compounds with different positioning of the acetyl groups was sufficiently different for a routine identification of mono- and diacetates of methyl beta-D- xylopyranoside and the corresponding 6-O-acetyl derivatives of methyl beta-D-glucopyranoside and other methyl hexopyranosides that were formed upon the action of esterases on the corresponding acetylated carbohydrate derivatives.